1. Field of the Invention
The invention relates to a driving element for an endless saddle chain, especially in the processing of printed matter, and a corresponding endless saddle chain.
2. Description of the Related Art
Saddle chains and drivers are found in saddle stitchers, where signatures are placed on and along the saddle chain by feeders and transported by the drivers to a stitching station. There, the signatures lying one on top of the other are stitched and then cut at three sides in a trimmer so as to produce a finished print product. The signatures used in saddle stitchers are folded sheets, having a single or several folds, that are placed on the saddle-shaped chain along the at least one fold.
Such saddle stitchers with corresponding saddle chains and driver components are marketed, e.g., by Heidelberger Druckmaschinen AG, under the type designation ST300, ST350 or ST400. Other configurations are known, e.g., European Patent EP 0 881 180 B1. Here, the driving elements are fixed to the ridge of the saddle chain, so that the saddle chain has a particularly narrow configuration. However, this has a drawback in that bearing blades arranged above the ridge must have a proper spacing from the feeders. Another known saddle stitcher is disclosed in European Patent Application EP 1 074 495 A1. Here, the driver elements are movably secured to the saddle chain so that they can swivel from a substantially vertical mounting position to a substantially horizontal mounting position.
As in other machines, the productivity of the machine does not depend primarily on the operating speed, but rather, on how many products can be processed with the machine in a specific amount of time. For saddle stitchers, one of the upper limits is the speed at which the saddle chain is driven, which is also associated with aerodynamic factors that make it difficult to transport the signatures lying loosely one on top of another on the saddle chain at higher speeds. In order to increase the number of products per unit of time and, thus, the productivity of the saddle stitcher without increasing the speed of the saddle chain, the chain pitch, i.e., the distance between the drivers on the saddle chain, is adjusted to the product size. Since a shorter spacing between the drivers on the saddle chain is sufficient for smaller products, by appropriately reducing this spacing, more products can be placed on the saddle chain per unit of time which increases the productivity. The problem with this in the prior art is that changing the chain pitch, if possible, is a costly operation, which in turn requires lengthy down time between jobs, which again reduces the productivity. Therefore, in some saddle stitchers, the saddle chain has saddle segments and receiver segments, and driver elements can be inserted in the receiver segments. The driver elements are polyurethane components which, due to their elasticity, remain form-fitted in the receiver segments and can be removed without the use of tools in order to change the pitch of the saddle chain. In practice, however, it has not always been possible to remove the driver elements from the receiver segments easily without the use of tools, since the driver elements often get jammed because of their configuration, and their removal can also result in damage to the driver elements and the saddle chain.